1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus which prevents a user from being exposed to a light from a light source.
2. Related Art
Generally, an image forming apparatus, such as a printer, a photo-copier, a facsimile machine and a multi-functional product, utilizes an electro-photographic method for image formation where an image is developed by applying developer to an electrostatic latent image formed on a photosensitive element by a potential difference and transferred to a printable medium such as paper to be formed, or an inkjet method for image formation where an image is formed by discharging ink onto a printable medium, through a multiplicity of inkjet nozzles, a dyes-sublimation method where an image is formed by selectively heating an ink ribbon contacting a printable medium and etc. Among these methods, the electro-photographic method is widely adopted to an image forming apparatus because of high printing speed, high resolution and low cost.
The image forming apparatus of the electro-photographic type comprises a paper feeding unit, a laser scanning unit (LSU), a developing unit, a fixing unit and a discharging unit. When the paper feeding unit supplies a printable medium such as paper, to the developing unit and the LSU scans a light source such as a laser, the developing unit selectively applies developer onto the printable medium to form a printed image. The fixing unit fixes the applied developer onto the printable medium by applying heat and pressure. The discharging unit then receives the printable medium with the developer being fixed from the developing unit and discharges the printable medium to the outside.
The developing unit is typically provided with a photosensitive element, a developing roller and a fixing roller. When the LSU scans laser onto the photosensitive element to form an electrostatic latent image, the developing roller develops an image by supplying developer to the latent image and the fixing roller transfers the developed image formed on the photosensitive element to a printable medium.
The LSU comprises a light source such as laser to scan light. A laser diode (LD) is typically used as a light source. In addition, a light emitting diode (LED) array in which a multiplicity of LED devices are disposed may also be used as a light source. If the light from the light source is exposed to the user, the light exposure may injure the user. Therefore, the light from such a light source needs to be effectively blocked to avoid exposure to the user, particularly, for example, when a cover of a main housing is open.
FIG. 1 is a side sectional view of a typical image forming apparatus. As shown in FIG. 1, the image forming apparatus 1 comprises a main housing 30, a cover 40, a developing unit 11 and a light scanning unit (LSU) 20. The main body housing 30 accommodates the developing unit 11 and the light scanning unit (LSU) 20. The main body housing 30 accommodates a paper feeding unit (not shown) for storing a stack of printable media, such as paper, and supplying the printing paper to the developing unit 11, a fixing unit (not shown) for fixing developer applied to the printing paper, a discharging unit for discharging the printing paper having a fixed image and etc.
The cover 40 is coupled to the main housing 30, via a hinge 42, to rotate to open/close the main housing 30. The cover 40 is provided for the main housing 30 to be opened/closed so that the inside of the main housing 30 can be opened during, for example, installation or removal of the developing unit 11, malfunction or repair. The developing unit 11 comprises a photosensitive element 13 and is installed to and removed from the main housing 30.
The light scanning unit (LSU) 20 comprises a light source 21 such as laser for scanning light to the photosensitive element 13 and a frame 22 supporting the light source 21. A polygon mirror, a scanning lens, a reflecting mirror and other lenses are disposed along a light traveling path between the light source 21 and the photosensitive element 13. A light blocking unit 24 is rotatably coupled to the frame 22 by the light blocking hinge 25. In addition, the light blocking unit 24 is disposed on the light traveling path, and comprises a light slit 26 which the light goes through. The light slit 26 passes or blocks the light from the light source 21 according to the position of the light blocking unit 24.
The cover 40 comprises a protrusion 41 to contact the light blocking unit 24 when the main housing 30 is opened. When the cover 40 closes the main housing 30, the protrusion 41 presses the light blocking unit 24 in order for the light slit 26 to be located at a position so that the light slit 26 passes the light from the light source 21. Accordingly, the light source 21 may scan the light to the photosensitive element 13 to form an electrostatic latent image. When the cover 40 opens the main housing 30, the light blocking unit 24 is released from the pressure of the protrusion 41, so that the light slit 26 moves to a position where the light from the light source 21 is blocked. As a result, the user's exposure to the light from the light source 21 can be prevented by blocking the light scanned from the light source 21 when the cover 40 is opened. Such an example image forming apparatus 1 is described in more detail in Japan Patent Publication No. 06-297755.
However, according to the image forming apparatus 1, there still remains the possibility of the exposure of the light from the light source 21. If the light blocking position of the light blocking unit 24 deviates from a proper position because of deformation of the light blocking unit 24 due to heat, fatigue or etc. or the light blocking unit 24 does not completely blocks the light from the light source 21, the user may be exposed to the light from the light source 21. Particularly, the light source 21 is required to scan light having a high output in order to enhance the printing speed. Accordingly, it is much more important to stably and effectively block the light from the light source 21 in order to prevent the user from being exposed to the light having the high output.